SET @value problem with ColumnStore

I have a customer complaining that setting SQL variables from ColumnStore takes a very long time.

For instance:

This is a ColumnStore table: `nucleus`.`neustar_pcp`;

This query:

SELECT COUNT(`HHRECID`) FROM `nucleus`.`neustar_pcp`;

Takes only milliseconds to run.

However this query:

SET @rowcnt = (SELECT COUNT(`HHRECID`) FROM `nucleus`.`neustar_pcp`);

Takes 1 minute and 47 seconds to run.